add

Additive Operator. The binary + operator performs addition when applied to two operands
of numeric type, producing the sum of the operands. If the type of either operand of a + operator is
String, then the operation is string concatenation.

If one of the operands is String, the returned value is the string concatenation;
The sum of two operands of numeric type. The left-hand operand is the minuend and the right-hand
operand is the subtrahend;